A software programmable CMOS telephone circuit

A mixed analog-digital IC combining the speech and signaling functions of an analog telephone is described. The realization in a standard 2- mu m CMOS process offers the possibility of integrating complex digital functions, such as dual-tone multifrequency (DTMF) generation, in combination with many digital programmable analog circuits . Novel features, such as digital programmable level control, DC characteristics, frequency response, input impedance, and sidetone path, are implemented. These attributes offer a flexible solution for the different international requirements, with only a few external components. Software control of analog and digital functions and the high degree of integration enable telephone manufacturers to produce a quality feature phone with a minimum of components, and therefore with high reliability and low cost.>